@▷ High Temperature Alarm Circuit | Diagram for Schematic

High Temperature Alarm Circuit

High temperature alarm system 300x139 High Temperature Alarm Circuit

This is the circuit design of high temperature alarm system. The circuit will warn us for any temperature higher than default setting which already predefined before. Temperature control is done by the thermistor TH1, which is a negative factor. The resistance varies between 10K Ohm at 25° C and about 1K Ohm at 94° C. The trimmer TR1 regulates the precise temperature at which the Q1-2, attached as Darlington, agoun, making the relay K1 to close and BZ, sound.

The alarm is activated when the temperature becomes higher than the default setup. The thermistor should be located away from the rest of the circuit, it is to prevent damage due to the heat. You can use 9V battery to operate this circuit, but if it is mounted in a fixed position, then we can use a fixed voltage power supply.

In the relay contacts, you can connect the load to switching the main power for a lamp or another circuits. It can also add an LED to sign and visual stimulation. The arrangement is by immersing the thermistor TH1, in the water which we know the temperature (contacts should be well insulated that they do not have short circuit) and adjusting the trimmer until the circuit is excited. The cable connecting the circuit with the TH1 must be shielded.

Components List:

R1 = 820 ohm
R2,R3 = 1Kohm
C1 = 220uF/16V
D1 = 5.6V 0.5W Zener
D2,D3 = 1N4148
Q1,Q2 = BC550C
TR1 = 2.2Kohm Trimmer
TH1 = Thermistor 10Kohm at 25° C
BZ1 = Buzzer
K1 = 6V 200 ohm Relay
S1 = 1x2 Switch
BATT = 9V Battery or external power supply
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